Power electronic modules are typically used as the building blocks of power converters, such as inverters for the control of electric motors. For example, within an aircraft such modules may be used within a converter which powers an all-electric starter-generator. Power electronic modules may be used in a wide number of industries including transport where it may be used in hybrid electric systems for aero, marine and/or land based transport. They can also be used within power generation industries as well as civil and military infrastructure. The modules described herein are generally applicable to any industry that uses power electronics.
Power electronic modules are typically mounted to a heat sink in order to facilitate heat transfer away from the semiconductor components of the modules.
Conventionally, power electronic modules have a number of substrate layers between the semiconductor components and the outside environment. These layers provide mechanical support, electrical isolation, electrical connection, protection and thermal management of the components. Typically the heat flux generated from losses within the semiconductor is directed downwards, through the many layers, into a heat sink.
For example, a substrate for a module may be formed with a ceramic layer (e.g. AlN) sandwiched between two metal layers (e.g. Cu metallization layers). The bottom metal layer can then be soldered to a metal-matrix composite (e.g. Al—SiC) baseplate, which in turn is connected to the heat sink.
A problem arises, however, that the number of substrate layers within the module present a significant thermal resistance and therefore limit the power handling of the semiconductors or can cause unacceptable heat rises. Particularly problematic can be the thermal interface materials used to create thermal connections between layers. There can also be reliability issues due to degradation of these interfaces.